Method of producing a silicon semiconductor device



March .1961 A. HERLET ETAL 2,974,074

METHOD OF PRODUCING A SILICON SEMICONDUCTOR DEVICE Filed Feb. 18; 1959 (Au Sb-As-O-S) ivmriroi) or immense A sILIcoN sEM-r p CONDUCTOR DEVICE Adolf Herle't aiid Hubert Pairing; Piet'zfld; Upper Franconia, and Norbert Sc'li'ihk Erlangen; Germany, assignors to sime'n's schlickertwerke Aktiengesell-i schaft, Berlin-Siemensstadt, Germany; a corporation of Germany Filed Feb; 1%, 195a, see Na; 79 L001 G laims pri'ority, application Germany Feb. 19; 1958 9 Claims; err ta-1.5

O'iii invention relates to e'l'eetr'ic semiconductor devices such as rectifiers, power transistors or photiodiodes', whose semiconductor body consists of substantiall monocr'ystalline silicon, and is an improvement wane-mama dis= closed and claimed in the copending' a'ppli'ca'tion of Norbe rt' Schink and Adolf Herlet Serial No. 71l,9 '6' 7, filed January 29, 1958, now US; PatentNo'i 2,959,501 assigned to the assignee' of the present. invention; More specifically, therefore, ourinven't'ion concerns the manunature of s'e'rni'conductoii devices in which the silicon crystal is'fusio'n-joined with a contaet electrode consisting of a gold-antimony alloy v'v O l to 5%, preferably about 1%, antimony and a trace content art s n-e th ainciiint Ofarsenie being betWeenQOO I' ahd-0; 1% related to total quantity of the gold-antimony al ltiis ncbjeet of our invention to further improve the" reliability and uniformity of the silicon semiconductor devices ride with the aid of a process of the type mentioned ab ve'.

In accordance with our invention we provi the g 161 antimony-arsenic alloy with" an additional trace content of oxidic oxygen before alloying the alloy together with, and into the adjacent surface Zone of the 'si mono crystal. By oXidic oxygen we mean oxygen present (if available as the oxide. 4 V I We have found that particularly eye-fa le result-s with respect to the absence of faults in th productsare obi tained if the oxygen addition is wee-a 0.'O1% and nearly 0.1% relating to the torn Weight ofthe" geld-amirnony-arsenic alloy. I

For adding the ox en, the quantity of antimony 0"1" a portion thereof, to be used for'forrning the alloy, is fir's't' roasted in pulverulent form within an oxygen-containing atmosphere, for example in air. Another irle'thod is" to first adrniX the arsenic to the antimony, and then for ast the quantity of antimony, or a portion thereof, required for forming the alloy, in prime-Intent form within'a'n oxygen-c'ontaining atmosphere, for example an. further way of adding'the oxygen is t'oprod'uce" a nay of'arseniccontaining antimony and oxyge neoma ifig antimony and then alloying this alloy togethefwith the pure gold in the proper proportions. -content can be incrementally increased during several Forthis purpose the gold successive melting processes whereby, an accurate dosage is more readily obtained. I [v t h According to the cop'ending appneafian of A'dolfi-Herlet, Hubert Pain ing and Norbert SEhink, serial No. 769,295, filed October" 24; 1958, new, s; Patent No. 2,937,113 and assigned" as tl'ijasisignee er the present irivention, the gold-antimony alloy to be a1 o'yed into" the silicon monocryst'al may be p'rdvidd trace 6atent of sulfur, preferably between 00001% and 0.1%- relating to the total weight of the gold-antimony alloy. such a trace content of s'ulfiiican also be additionally provided in the rnetlidd according" to (represent avention. or this" urpose; for example, a" pfe-ano earl be prepared frorii' dinner: kinds of antimony; remedy of United States g r 2,974,074 7 I Patented Mar. 7, 196} ice 2 sirens-emailing antimony, oxygen-containing niony, and sulfur-containing antimony. This pr 'all'oy is their alloyed together with pure gold preferably in a stepwise manner as described above.

An embodiment of producing an alloy according to the invention will be described presently. The' fprdces"s" is carried out by first preparing three difiere'n't kinds of antimony, A, B and C.

Antimony A v 95 grams antimony re iiilted together with 5 alrs'e'iiic at approximately 610 0.

. Antimony B I 100 grams antimony powder are roasted in air at a gradually increasing temperature and are thus heated iip'fto melting temperature of approximately 635 C; After cooling the oxygen-containing antimony, the oXygen content is determined by analysis. on the verage; an oxygen content of 2% will be determined; However; departures from this value may occur, for eXaiiiple'du todiif'erences' in the granulation of the antimony powder; dilferen'ces in the duration or program of the heating? process, or differences in the amount of the maximum temperature being reached.

Anrimen C p 100 grams antimony powder are melted together with 2- grams flowers of sulfur by heating at about 635 C. The sulfur content is determined bytanalysis. It is as'-' sum-ed, for example, that a sulfur content of 1% is thus found: However, departures from this value may also occur as a result of the differences in the performance of the melting process mentioned in the foregoingparagraph.

For obtaining'the'correct proportion of' the various additions to be made to the gold-antimony alloy ready for use; suitable quantities of the antimony kinds, A, B and- C are melted together with an additional quantity of pure antimony at a ternpratureof approximately 635 d C-. By calculation, the following weight proportions are determined for the example dealt with above:

In this manner, there is obtained an antimony-arsenioxygen-sulfur alloy with 0.1% arsenic,- 1'% oxygen and (11% sulfur. A portion of this pre-allo'y, for example 100 grains, are melted together with 300 grams pure gold at about 360 C; This mixing proportion corresponds to the Au/Sb eutectic with a content of 25% Sb. When 4Q0 grams of thiseutectic alloy are melted together with 9600 grams pure gold at about 1100" (3., the resulting composition in the amount of 10 kilogramconsists of ready-for-nse gold-antimony alloy with the desired trace contentsof added elements. The necessary quantities re quired for alloying the metal into the silicon rnonocrystals can then be taken from this Supply; For this purpose it is preferable to roll the above-mentioned goldant-imony alloy into the form of foils. This can be done without particular difiiculty with an alloy' containing the above-stated quantities of individual alloy components.

For the production of rectifi'ers it had been found ad'-' vantageous to roll' t-he fo'il thickness down to ab'OutOL-T mm. For the production oftransistors, foils rolled down to a thickness 0-f about 0.04 n1m.'have been found to be favorable.

. It is preferable to perform the above-described melting t processes in' an atmosphere of inert gas; for exampleargon, nitrogen or carbon monoxide, because otherwis'e' 'the desired dosage of the respective additions; under certain in which the antimony content of the melt is very small in comparison with the eutectic Sb/Au ratio of 25%.

Tests have shown that, inconjunction with the abovedescribed trace additions of oxygen and/or sulfur, the arsenic content can be reduced down to one order of magnitude smaller than stated in the example, namely down to 0.0001% of the total quantity of the goldantimony alloy, without appreciably decreasing the desired result.

The method of joining of the electrode with the silicon body by the formation of a diifusion alloy at the boundary zone is described in detail in our copending application Serial No. 711,967. One such method is effected by assembling disc-shaped silicon bodies on both sides with electrode foils located in face-to-face area contact therewith. Any desired carrier plates may also be assembled by placing them onto the foil electrodes. The entire assembly is then placed between pressure plates, for instance of graphite, and is clamped between these plates while being heated to a temperature between about 700 and 800 C. for approximately to minutes. This suffices to produce the desired alloyed fusion joint between the silicon body and the electrode foil according to the invention. Another method of joining the electrode with the silicon body is described in the copending application of R. Emies, Serial No. 637,029, filed January 29, 1957, and assigned to the assignee of the present invention.

Illustrated on the drawing, by way of example, is a silicon rectifier made according to the present invention. The rectifier comprises a monocrystalline semi-conductor body 1 of p-conducting silicon, shaped as a flat cylinder of approximately 0.4 mm. thickness and a diameter of approximately 10 mm. Joined with the top surface of the silicon crystal is an electrode 2 of gold foil containing approximately 99% gold, approximately 1% antimony, a trace of arsenic amounting to about 0.01%, a trace of oxidic oxygen-amounting up to about 0.01%, and may also contain a trace of sulfur amounting up to about 0.1%. The foil 2 has a thickness of about 0.05 mm. and a diameter of approximately 9 mm. Joined with the bottom surface of the silicon body 1 is an electrode 3 of aluminum having a foil thickness of approximately 0.05 mm. and a diameter of approximately 9 mm. Both electrodes are fushion-joined with the silicon body by one of the methods described above, so that an .alloyed merger zone exists between each electrode and the semiconductor body, the alloy penetrating and diffusing somewhat into the silicon body. A barrier layer is formed in the boundary zone between the gold-alloy electrode 2 and the silicon body 1 so that the device has a symmetrical conductance.

A gold-antimony-arsenic-oxygen alloy according to the invention may also be used for producing a barrierfree junction. In this case, the silicon body must have n-type conductance. It will also be understood that various other metals, forming barrier-free contacts may be used as counter-electrode instead of aluminum foil 3.

It will be obvious to those skilled in the art, upon a study of this disclosure, that this invention permits of various modifications and alterations with respect to the individual method steps disclosed, and hence can be embodied in equipment other than as particularly illustrated and described herein, without departing from the essential features of the invention and within the spirit and scope of the claims annexed hereto.

We claim:

1. The method of producing an electric semi-conductor device having a substantially monocrystalline silicon body and an electrode on said body, which comprises forming an alloyed composition of gold, antimony and traces of arsenic and oxygen in amounts between about 0.2 and 5% antimony and about 10- to about 10 arsenic, and containing a trace of oxidic oxygen in an amount between 10- to about 10' d!' being substantially all gold; and alloying the composition together with the silicon body to form an area fusion joint between said body and said electrode.

2. The method according to claim 1, including the step of roasting antimony in pulverulent form within an oxygen-containing atmosphere'at a temperature of approximately 635 C. to introduce said oxidic oxygen content.

3. The method according to claim 1, including the step of roasting arsenic-containing antimony in pulverulent form within an oxygen-containing atmosphere at a temperature of approximately 635 C. to introduce said oxidic oxygen content.

4. The method according to claim 1, including the steps of first forming a pre-alloy from arsenic-containing antimony and oxygen-containing antimony and thereafter alloying said pre-alloy with substantially vpure'gold.

5. The method of producing an electric semi-conductor device having a substantially monocrystalline silicon body and an electrode on said body, which comprises forming an alloyed composition of gold, antimony and traces of arsenic and oxygen in amounts between about 0.2 and 5% antimony and about 10- to about 10 arsenic, and containing a trace of oxidic oxygen in an amount between 10- to about 10" the remainder being substantially all gold, and including the steps of first forming a pre-alloy from arsenic-containing antimony and oxygen-containing antimony and thereafter alloying said pre-alloy with substantially pure gold, stepwise increasing the quantity of said gold by adding portions of gold in a plurality of melting processes.

6. The method of producing an electric serni-conductor device having a substantially monocrystalline silicon body and an electrode on said body, which comprises forming an alloyed composition of gold, antimony and traces of arsenic and oxygen in amounts between about 0.2 and 5% antimony and about 10- to about i0- arsenic, and containinga trace of oxidic oxygen in an amount between 10* to about 10- the remainder being substantially all gold; and alloying the composition together with the silicon body to form an area fusion joint between said body and said electrode, and including the step of providing said oxygen-containing gold-antimony-arsenic alloy with a trace content of sulfur in an amount between 10- and 10- prior to alloying said composition together with the silicon body.

7. The method of producing an electric semi-conductor device having a substantially monocrystalline silicon body and an electrode on said body, which comprises forming an alloyed composition of gold, antimony and traces of arsenic and oxygen in amounts between about 0.2 and 5% antimony and about 10- to about 10- arsenic, and containing a trace of oxidic oxygen in an amount between 10- to about 10 the remainder being substantially all gold, and including the steps of first forming a pre-alloy from arsenic-containing antimony, oxygencontaining antimony ad sulfur-containing antimony, and thereafter alloying said pre-alloy with substantially pure gold, stepwise increasing the quantity of said gold by adding portions of gold in a plurality of melting processes.

8. The method of producing an electric semi-conductor device having a substantially monocrystalline silicon body and an electrode on said body, which comprises forming an alloyed composition of gold, antimony and traces of arsenic and oxygen in amounts between about 0.2 and 5% antimony and about 10- to about 10- arsenic, and containing a trace of oxidic oxygen in an amount between 10- to about 10- the remainder being substantially all gold, and including the steps of first form ing a pre-alloy from arsenic-containing antimony by melting approximately antimony with about 5% arsenic in an inert atmosphere at approximately 610 C. to form an antimonyarsenic alloy, roasting a quantity of powder containing a major amount of antimony in an oxidizing atmosphere at a temperature of approximately 635 C. to form an oxygen-containing antimony material, melting '5 a further quantity of antimony together with sulfur to form a sulfur-containing antimony material, combining approximately two parts by weight of said antimonyarsenic alloy, approximately 50 parts by weight of said oxygen-containing antimony material, approximately 10 parts by weight of said sulfur-containing antimony, and approximately 38 parts by weight of pure antimony by melting said proportionate parts in an inert atmosphere at a temperature of approximately 635 C. to form said preal loy, melting a portion of said pre-alloy with pure gold at a temperature of approximately 360 C. to form a gold-antimony eutectic alloy, subsequently melting said eutectic alloy in an inert atmosphere with a further quantity of pure gold at a temperature of approximately 1100 I taining between 10- and 10- of an element selected C., to form a further gold-antimony alloy, rolling said 15 last mentioned alloy down to foil thickness; and alloying said foil. together with the silicon body to form an area fusion joint between said body and said electrode.

-9. The method of producing an electric semi-conductor device having a substantially monocrystalline silicon body and an electrode on said body, which comprises forming an alloyed composition of gold, antimony and a trace of arsenic in amounts between about 0.2 and 5% antimony and about 10' to about Illarsenic, and confrom the group containing oxygen and sulfur, the remainder being substantially all gold; and alloying the composition together with the silicon body to form an are-a fusion joint between said body and said electrode.

2,809,165 Jenny v.. Oct. 8, 1957 Logan et a1. Mar. 24, 1959 

1. THE METHOD OF PRODUCING AN ELECTRIC SEMI-CONDUCTOR DEVICE HAVING A SUBSTANTIALLY MONOCRYSTALLINE SILICON BODY AND AN ELECTORDE ON SAID BODY, WHICH COMPRISES FORMING AN ALLOYED COMPOSITION OF GOLD, ANTIMONY AND TRACES OF ARSENIC AND OXYGEN IN AMOUNTS BETWEEN ABOUT 0.2 AND 5% ANTIMONY AND ABOUT 10-4 TO ABOUT 10-1% ARSENIC, AND CONTAINING A TRACE OF OXIDIC OXYGEN IN AN 